Preheat the oven to a low temperature such as 150 degrees Fahrenheit and turn it back off.
Open up the oven and place a large oven-safe dish of boiling water on the bottom rack and an oven-safe bowl with 1/2 cup of ammonia in it on the top rack.
Close the oven door and leave the ammonia and water in the oven overnight.
Open up the oven and remove the dish of water and dish of ammonia.
Drizzle grease-cutting dish soap onto a dampened sponge and use it to wipe away the burnt grease from the inside of the oven door.
Rinse the door off with a damp sponge or cloth.
Pour plain white vinegar into a spray bottle.
Spray the greasy area with the vinegar and let it soak for 15 to 20 minutes. Keep spraying the area every few minutes to keep it damp and keep a paper towel on the floor below it to absorb vinegar as it trickles down to the floor.
Dampen a sponge with warm to hot water.
Dip the sponge in grease-cutting dish soap and wipe away the grease.
Rinse the area with a damp cloth to eliminate residual grease and soap before wiping the door dry with a clean, dry towel.